The invention relates to a particle-accelerating electrode designed as a Faraday cage structure and inside of which a blanking system is provided for blanking a particle beam.
It is standard in electron beam measuring technology to register high-frequency events at a measuring location with the assistance of stroboscopic measuring methods. Given a stroboscopic measuring method, an electron beam or, in more general terms a particle beam, is gated synchronously with the high-frequency event at a measuring location such that the particle beam senses the measuring location and thus triggers measured signals only during a fraction or during a plurality of fractions of a period duration of the high-frequency event at the measuring location. This occurs during each and every period of the high-frequency event at the measuring location. Stroboscopic measuring methods are preferably executed in scanning electron microscopes. Since the particle beam must be keyed in and blanked out given stroboscopic measuring methods, a particle beam blanking system is required in a stroboscopic measuring apparatus. Such a particle beam blanking system is usually provided as part of a beam generating system.
A blanking system for a particle beam is known from U.S. Letters Pat. No. 4,169,229, incorporated herein by reference, wherein the particle beam is shaped after its emission with the assistance of a Wehnelt electrode and then passes an accelerating electrode designed as an apertured disk. After passage through this accelerating electrode, the particle beam impinges a first pin diaphragm, passes through the actual deflection system which comprises two symmetrical deflector plates, passes through a further pin diaphragm, and finally enters a vacuum tube through a third apertured disk secured to the vacuum tube. Since this known apparatus for blanking a particle beam is extended in the direction of the particle beam, the incorporation of such a blanking system in a particle beam apparatus requires a lengthening of the particle-optical column by introducing an additional ring into the particle-optical column. Such an apparatus, moreover, is difficult to manipulate, since many different piece parts must themselves be respectively dismantled when replacing such an arrangement or when merely removing such an arrangement from the particle-optical column. As a consequence of the many different piece parts, involved adjustment systems are required, these making the overall apparatus relatively expensive. The overall arrangement, moreover, requires many individual pin diaphragms or apertured disks in order, on the one hand, to meet particle-optical requirements and, on the other hand, in order to enable a good vacuum seal. Given this known apparatus, the entire blanking system is accommodated in a vacuum-tight housing together with the beam generator.
A particle beam generating system is known from German patent application No. P 32 04 897.1, incorporated herein by reference, which comprises a particle-accelerating electrode designed as a Faraday cage and in whose interior a blanking system is attached for blanking a particle beam. This known particle beam generating system is designed such that it permits an optimum beam value or brightness and an optimum centering for a specific accelerating voltage. Since the patent application states nothing with respect to a required vacuum seal of the particle beam generating system, it is assumed that this particle-accelerating electrode is also integrated into the particle-optical beam path together with the blanking system in a fashion that is standard according to the prior art. Since, due to the blanking system, the particle-emitting electrode has a considerable extent in the direction of the particle beam, the particle-optical column must be lengthened in comparison to a particle beam system without the blanking system. This usually occurs by means of an additional introduction of a ring into the particle-optical column. As in the aforementioned apparatus, moreover, additional apertured disks or pin diaphragms are required for the vacuum seal, these resulting in a considerable expenditure for additional adjustment systems.